Laser annealing (also called laser spike annealing, laser thermal annealing, laser thermal processing, etc.) is used in semiconductor manufacturing for a variety of applications, including for activating dopants in select regions of devices (structures) formed in a semiconductor wafer when forming active microcircuits such as transistors and related types of semiconductor features.
The laser annealing process typically takes place under vacuum in a process (or reaction) chamber, such as the microchamber discussed in U.S. Pat. Nos. 5,997,963 and 9,029,809. One reason for using a vacuum is to reduce the amount of oxygen gas present at the surface of the semiconductor wafer being processed because the oxygen gas is highly reactive and will oxidize the surface of the semiconductor wafer. This is especially true at the high temperatures associated with laser annealing since the higher temperatures increase the rate of oxidization.
Under normal vacuum conditions, the oxygen gas concentration in the interior of the process chamber can be reduced to about 50 parts-per-million (ppm) (vol.). Reducing the oxygen gas concentration further is problematic and requires expensive equipment (e.g., a more powerful vacuum pump), and as well as substantial modifications to the process chamber.
It is therefore desirable to have a low-cost and simple way of reducing the amount of oxygen gas at the surface of the semiconductor wafer being laser annealed beyond what can achieved using conventional vacuum-based approaches.